1. Field of the Invention
The present invention relates generally to a method of producing a head core for a magnetic head, and more particularly to a technique for easily forming a track in the head core with high dimensional accuracy, to produce a desired magnetic head.
2. Discussion of the Prior Art
Magnetic heads are conventionally widely used in a video tape recorder (VTR), floppy disk drive (FDD), hard or rigid magnetic disk drive (HDD/RDD) or the like, to effect information recording on and reproduction from a magnetic recording medium such as a magnetic tape or magnetic disk. As known in the art, the magnetic head has a head core formed of a magnetic material such as ferrite. The head core has a coil-winding groove around which an annular or closed magnetic path is formed, and a magnetic gap having a suitable minute spacing for writing or reading information on or from a magnetic recording medium. The magnetic gap is formed in a medium-sliding surface (magnetic disc sliding surface) of the head core which is to be opposed to the recording medium and on which the recording medium slides in operation, such that the magnetic gap intersects the annular magnetic path. The head core is also formed at its medium-sliding surface with a track whose width determines the width of the magnetic gap, such that the track extends across the magnetic gap, in a sliding or running direction of the recording medium relative to the head core.
The magnetic head core used for VTR, FDD or the like is conventionally fabricated in the following manner. Referring first to FIG. 1, a pair of ferrite blocks (core bars) 2, 4 are ground by a dicing cutter, for example, using a diamond blade or grinding stone, so that beveled grooves 6 for defining the width of tracks are formed in the ferrite blocks 2, 4. Then, the grooves 6 are filled with glass fillers 8, and the opposed surfaces 10 of the ferrite blocks 2, 4 which cooperate to define magnetic gaps are ground. Thereafter, the ferrite blocks 2, 4 are joined together with a gap spacer interposed therebetween, to provide a ferrite bar having a magnetic gap 12 whose size is determined by the spacer. The ferrite bar is then cut into core chips (16), one of which is shown in FIG. 1. The thus obtained head core 16 has a track 14 defined by the opposite grooves 6, 6, and a coil-winding groove 15 around which an annular or closed magnetic path is formed.
The above-described known method of producing the head core requires cumbersome process steps for forming the track 14. To control the width of the track 14 to about 20 .mu.m with an accuracy of .+-.1 .mu.m, for use with a VTR, for example, the beveled grooves 6 for defining the track width need to be formed by machining with an extremely high accuracy, using expensive precision machine tools. While the two ferrite blocks 2, 4 are to be butted and bonded together to form the track 14 having a target width "Tw", as shown in FIG. 2(a), this target width "Tw" may not be actually achieved due to a slight positional deviation or misalignment of the butted ferrite blocks 2, 4, as shown in FIG. 2(b) wherein the track 14 has a width of "Tw'" which is smaller than the target value "Tw".
To produce a magnetic head core used for HDD, on the other hand, a core slider body 20 having a suitable magnetic gap 18 is first prepared, as shown in FIG. 3, and two grooves 22 are then formed in the slider body 20 by grinding, so that a track portion 24 having beveled side faces and two air bearing portions 26 are formed on the slider body 20. Then, the beveled side faces of the track portion 24 are subjected to a grinding operation using a cup-shaped grinding wheel 28, so as to form a track 30 having a desired track width of "Tw", as shown in FIGS. 4(a)-4(c). The air bearing portions 26 are ground in a similar manner, to form air bearing surfaces 27, 27 on the opposite sides of the track 30. The thus ground slider body 20 is further processed to form a head core portion having the gap 18 and a chamfered leading ramp, so as to provide a core slider 31 (FIG. 3) having the integrally formed head core portion and slider portion with the air bearing surfaces 27.
In the thus produced core slider 31, the accuracy of the width of the track 30 is at its best kept to about .+-.1 .mu.m. Even this accuracy is extremely difficult to be guaranteed in the mass production of this type of core slider. Further, it becomes increasingly difficult to provide a sufficiently narrow track whose width is 10 .mu.m or smaller and has an accuracy of .+-.10%, so as to meet the recent requirement for high-density recording on a magnetic recording medium.
In the magnetic head cores as described above, the relatively narrow track 14, 30 is only required to extend over a length enough to cover the region adjacent to the magnetic gap 12, 18, i.e., the ferrite portions defining the gap 12, 18. According to the above known method, however, the narrow track 14, 18 extends over an unnecessarily large length to cover not only the region adjacent to the magnetic gap 12, 18 but also ferrite portions on the longitudinally opposite sides of the region, whereby magnetic saturation tends to occur upon formation of a magnetic field, rendering the resulting magnetic head unsatisfactory in terms of operating efficiency.